Harnessing the Power of RosBREED: Development, Validation, and Application of DNA Tests for Predicting Peach Fruit Quality, Disease Resistance, and Other Valuable Traits for Rosaceae Tree Fruit

DNA tests that predict valuable trait levels are essential for widespread adoption of marker-assisted breeding (MAB) of rosaceous tree fruits. The RosBREED project has facilitated development of PCR-based DNA tests for valuable traits in peach, apple, and sweet cherry, including peach fruit quality and disease resistance. Based on quantitative trait loci (QTLs) discovered on peach chromosomes 7, 3, 4, 1, and 6, by RosBREED collaborators for fruit sweetness and acidity, blush, slow ethylene production, and fruit bacterial spot resistance, respectively, DNA tests were developed at Washington State University in collaboration with the University of Arkansas (UA) and Clemson University (CU) peach breeding programs. These tests resulted from successful conversion of single nucleotide polymorphism haplotypes into simple sequence repeat (SSR) markers.  The trait predictiveness of four tests, G7Flav-SSR (for flavor), Pp-MYB10-SSR (skin blush), Xap-SSR (bacterial spot resistance), and SMF-SSR (slow-melting flesh) were confirmed on standard cultivars and UA and SC germplasm. The DNA test G7Flav-SSR differentiated low (L), medium (M), and high (H) sweetness and acidity alleles; Pp-MYB10-SSR differentiated low (bl) and high (Bl) blush alleles; Xap-SSR differentiated susceptible (S), intermediate (I), and resistant (R) bacterial spot alleles; and SMF-SSR differentiated alleles for slow (B) and fast (A) ethylene evolution after harvest. Validation of these DNA tests was conducted on unselected, independently phenotyped families. All four tests were refined for high-throughput genotyping. In 2014, this suite of DNA tests along with flesh type (endoPG-6) and fruit acidity (CPPCT040B) markers were used for marker-assisted seedling selection in the UA program. This advance in DNA-informed breeding represents an example of successful collaboration among institutions and across disciplines. Other DNA tests emerging from RosBREED include those for the prediction of peach maturity date and mealiness, apple acidity, sweetness, and firmness, and sweet cherry maturity time, blush, and firmness. By harnessing the power of collaboration, specifically the integration of pedigree, phenotypic, and genotypic data generated by RosBREED team members for QTL discovery, the development of breeding-relevant DNA tests was possible. Tools such as the DNA tests developed during the course of this project are now available to make DNA-based predictions a routine part of tree fruit breeding.